Generally speaking, a maximum workable frequency Fmax that can be reached by a digital integrated circuit is related to a circuit physical property P (which is influenced by factors such as a manufacturing process and aging), a working voltage V and a working temperature T, that is, Fmax=f (P, V, T).
With continual decreasing of a line width of the digital integrated circuit, on one hand, the randomness of a chip manufacturing process is increased, where circuits of a same design, after being manufactured, have circuit physical properties P that are distributed wider; on the other hand, Fmax of a same physical circuit is more sensitive to a change in parameters such as the voltage V and the temperature T. The above two aspects both causes that the maximum workable frequency Fmax of the digital integrated circuit is distributed in a wider range.
Currently, a clock source used by the digital integrated circuit, that is, a clock generation circuit, whether it is a crystalloid, an oscillator or a TCXO (Temperature Compensate X'tal (crystal) Oscillator, temperature compensate x'tal (crystal) oscillator) which is mounted outside a chip of the circuit, or it is a PLL (Phase Lock Loop, phase lock loop), a DLL (Delay locked loop, delay locked loop), or a frequency divider circuit which is inside a chip, aims at a stable frequency, that is, does best to keep a frequency of an output clock signal unchanged under different parameter distribution conditions of the circuit physical property, the working temperature, and the working voltage.
However, under a circumstance that parameter conditions of the circuit physical property, the working temperature, and the working voltage are dispersed, if the digital integrated circuit is required to work in a constant frequency, it is a must to set a working frequency of the digital integrated circuit to be a frequency at which the digital integrated circuit is capable of working under most unfavorable parameters so as to ensure the circuit to work stably. For example, the working frequency of the digital integrated circuit is set to be a working frequency under a maximum working temperature, a minimum working voltage or a poorest circuit physical property (such as a poorest producing process). The maximum workable frequency of the digital integrated circuit under typical parameters is far higher than the working frequency under most unfavorable parameters, and therefore the working manner restrains the potential of the digital integrated circuit from being fulfilled, limits performance of the digital integrated circuit, and may cause an increase in power consumption of the digital integrated circuit.